There are well known issues as regards the necessity of providing a device for adjusting the usable length of a bracelet.
On the one hand, in the case of bracelets formed of links, the wrist circumference of the user may have a value that falls between two configurations of the bracelet which differ from each other by a single link. Therefore, it is useful to provide a device for adjusting the usable length of the bracelet that allows a finer adjustment of the bracelet length than the removal or addition of a link.
On the other hand, it is also known that wrist circumference value varies with the season, with the maximum value generally being attained in summer and the minimum value being attained in winter. Here too, it is preferable to provide a fine adjustment device for the usable length of the bracelet that enables the person wearing the bracelet to adjust the length to improve the wear comfort thereof.
By way of example, EP Patent Application No 09131060 A1 discloses a clasp with an unfolding buckle comprising a cover with a series of pairs of holes for housing the ends of a bar for attaching a bracelet. Two adjacent pairs of holes are separated by a distance defining one adjustment pitch of the usable bracelet length, to answer the aforementioned problems.
However, this type of device for adjusting bracelet length is unattractive given that the adjusting holes are visible on the sides of the cover. Further, the adjustment of this type of clasp requires some dexterity since a pointed tool has to be inserted in the holes to compress the bar securing the bracelet, which is likely to lead to damage to the cover if the person performing the adjustment is clumsy.
To avoid this situation, alternative devices have already been disclosed, such as for example in EP Patent No 0350785 B1 which discloses a similar clasp to the above but comprising, by way of alternative, a device for adjusting the usable length of the bracelet that can be operated without using a tool. Indeed, the clasp disclosed in that Patent is of the type with an unfolding buckle comprising two strips hinged to each other by means of a pin that passes through both, each of the strips carrying at the end thereof a fastening member to a bracelet. A first strip carries a hook intended to be engaged in a hole arranged in the second strip to cooperate therein with a spring catch for locking the hook, and therefore the clasp, in a closed state. The second strip includes two portions capable of sliding in relation to each other within a predefined range, defining an adjustment pitch of the usable length of the bracelet. The first of these two portions carries the hinge connecting it to the first strip while the second portion carries the locking spring catch. The hole in which the hook engages to lock the clasp has a length, along the longitudinal direction of the bracelet, which equates to the sliding range of the two portions of the second strip. The spring catch has a central portion defining two sites for the hook, along the longitudinal direction of the bracelet, providing two different usable lengths of the bracelet. A control member including, in particular, a pusher, can actuate the spring catch to release the hook and open the clasp.
It should be noted that one drawback which results from this structure is the loss of bracelet length adjustment each time that the clasp is opened. Consequently, each time the clasp is closed, the wearer of the bracelet has to check that the hook is inserted on the side of the central spring catch portion matching the desired bracelet length.
Adjustment devices comprising a specific locking member have also been proposed, by way of alternative, to avoid this type of drawback.
EP Patent Application No 1378185 A1 provides one such example.
However, these devices generally have complex, conspicuous designs since they can comprise at least one control member used for locking the clasp, at least one additional control member for locking the adjustment device and generally at least one elastic return member.